The long range objective of this research is the understanding of the molecular mechanisms that underlie the formation of specific connections in the developing nervous system. Specific cues associated with the cell surfaces of the pre- and post-synaptic cells may be involved in cell-cell recognition, and in the formation and maintenance of the synapse. The time course of appearance of such cues during development is still not known. I propose to study specific cell-surface antigens, one of which is common both to the neurons of the embryonic chick ciliary ganglion and to a subpopulation of mesencephalic neural crest cells (the mesencephalic crest is the source of cells for the developing ganglion). No other neuronal or non-neuronal cells from the embryonic chick tested expressed this antigen. Its presence was discovered through the use of highly specific monoclonal antibodies raised in mice immunized with cultured ciliary ganglion neurons. The specific objectives of this proposal are to discover if the antigen plays a functional role in development or in synapse formation. The monoclonal antibody can be used to study its function and to characterize it biochemically. Because the antibody is cytotoxic for the ciliary ganglion neurons and for the subpopulation of neural crest cells, attempts will be made to ablate the ganglion by destroying the presumptive precursor population with antibody and complement before the neural crest cells begin to migrate. Other monoclonal antibodies are being tested that will assist in the study of cholinergic functions in embryonic neurons. These antibodies have been made in mice immunized with Choline acetyltransferase (CAT) and acetylcholinesterase (AChE) the enzymes responsible for the synthesis and degredation of acetylcholine (ACh) the transmitter at both the ciliary neuronal cells and at the vertebrate neuromuscular junction. These studies may provide information about the molecular basis for neuronal identity and function and may also serve as reference points from which to direct studies of neural, neuromuscular diseases or birth defects.